The present invention relates to an ozone generator and a method for generating ozone by exposing oxygen to a high frequency alternating current with high voltage over a dielectric.
Ozone has strongly oxidizing features and is used, preferably diluted, to sterilize water. For example may wastewater be treated for purpose of breaking down or eliminating substances dangerous for the environment or the health as well as unpleasant smells from the water, and the drinking water may be pre-treated for purpose of improving the water quality. Other fields of application are e.g. as bleaching agent in the paper industry, for air purification purposes, and to perform certain oxidizing reaction in organic chemistry.
Ozone mixed with oxygen is produced by passing oxygen gas or gas rich in oxygen through an electric discharge. Oxygen gas or gas rich in oxygen is thereby made to flow through a chamber in an ozone generator or ozonizer, which chamber either is delimited by two tubes having the same axis or by plates in series, between which an electric discharge occurs. In this description the expressions space and chamber are used as representing the same, i.e. the place in the ozone generator where existing oxygen gas or gas rich in oxygen is converted to ozone.
The first mentioned type of ozone generator is for industrial purpose very large and space demanding and also difficult and expensive to produce and maintain. The second type of ozone generator is more economic and less space demanding, but has still certain sealing and strength problems and does not operate optimally.
A problem related to ozone generators is connected to that the chamber in which the oxygen in the form of oxygen gas or gas rich in oxygen is converted to ozone at least has one delimiting surface constituted of a dielectric material, a dielectric. This dielectric is utilized for the purpose of generating a corona at the discharge between a high voltage electrode and earth, and is generally composed of a ceramic or a glass material. High gas pressures and not the least pressure variations in the gas supplied to the chamber, for example caused by pressure shocks in the system when the gas supply is engaged or disengaged, generates high stresses on the ceramic with the consequence of the ceramic risking to crack.
Another problem is related to the sealing required between said dielectric and the opposite delimiting surface of the chamber, which opposite surface generally constitutes electric earth. This sealing is exposed to the influence of high gas pressure and pressure shocks. In addition the sealing is a problem for the useful life and the reliability of the ozone generator since ozone is particularly reactive, whereby common rubber gaskets tend to break down and cause leakage.
Concrete exemplary embodiments of ozone generators have been described in a manifold of publications, i.a. in the following:
In U.S. Pat. No. 5,354,541 A1 is thus a tubular ozone generator described comprising i.a. a helical spring electrode 12, a tube 14 of dielectric material surrounding the electrode 12 and also a tubular, earthed and cooled second electrode 15. Between the second electrode 15 and the tube 14 is an annular chamber 16 for ozone generation delimited. Supply of oxygen to the only annular chamber 16 for ozone generation occurs one-sided, whereby in the beginning also the pressure influence is one-sided. During operation a pressure influence is continuously present from the outside against the tube 14, and this pressure influence varies instantaneously by pressure shocks, which may occur during the operation. Altogether this causes major stresses on the construction and major risk for damages and leakage.
In U.S. Pat. No. 4,960,570 A1 a complex and material demanding ozone generator is described with i.a. tubes 3,8 of a dielectric material, alternatively tubes having an outer coating of dielectric material. The tubes 3,8 have internally a metallic film 4 constituting one electrode, alternatively show a separate electrode 10 inside the tubes 3. The tubes 3 are located between two flat external electrodes 1,2, which are cooled. Spaces or chambers 6 and 11, respectively, for ozone generation are found between the tubes 3 and the plate electrodes 1,2, and possibly also in the tubes 3 between the inside of the tubes and the electrode 10 therein. It is not evident from the publication how the spaces 6, between the details 3,8 of dielectric material and the cooled electrodes 1,2, are supplied with oxygen for ozone generation, and consequently nor how these details are affected by the pressure from the supplied oxygen or by pressure shocks arising during operation.
Through WO, A1 9701507 an ozone generator is known, which comprises two plates 2 of a dielectric material, and between them is a thread or net shaped electrode 3 located, over which electrode 3 is a high frequency alternating current with high voltage is applied and, on the outside of the plates 2, earthed and cooled electrodes 4. A space for ozone generation is delimited between the plates 2 and a frame 3xe2x80x2. The ozone generator is, from the inside of the space for ozone generation, exposed to pressure influence, whereby the plates 2 tend to separate. Instantaneously, at pressure shocks, this pressure influence may increase. Major risks for damages and sealing problems for the ozone generator exists. There are no spaces for ozone generation outside the plates 2.
In U.S. Pat. No. 5,435,978 A1 is finally also a flat ozone generator with two electrodes 1 described, which intermediately form a space 2 for ozone generation. On the respective electrode 1 a layer of dielectric material is applied. In order to compensate the pressure in the internal space 2 for ozone generation, an external pressure is applied on the ozone generator by locating it in a pressure vessel, in which a gas under pressure is supplied. Instantaneous pressure differences due to pressure shocks, which occur during operation of the ozone generator, are however hard to handle. The risk for damages is large at these occasions. Yet another ozone generator design is shown in xe2x80x9cHigh Density Ozone Generation In a Very Narrow Gap By Silent Dischargexe2x80x9d by M. Kuzumoto, Y. Tabata and S. Yagi, Mitsubishi Electric Corporation, from the 12th World Ozone Congress, May 15-18, 1995, Lille, France, Vol. 2, pages 51-58. The proposed design discloses a thin circular one-sided discharge chamber between a ceramic plate and an earth electrode. Gas inlets to the chamber are arranged in the periphery of the chamber, while an outlet is arranged in the center of the chamber through a hole in the earth electrode. The ceramic plate rests, on the opposite side of the chamber, against a stress buffering plate of unknown kind, which in its turn is adjacent to a metal plate. Towards the stress buffering plate the ceramic plate is coated with a metal layer, which forms a high voltage electrode. The depth of the chamber is defined by a metal spacer located therein and comprises radially extending support element.
A purpose with the present invention is to provide an ozone generator and a method for ozone generation, which overcomes the problems with the prior art. An aspect of this purpose is to use a simple, compact and less costly design to increase the power and improve the conversion efficiency compared to known ozone generators, and moreover to prevent components of the apparatus to be damaged or to deteriorate in efficiency due to the overpressure of supplied gas and due to pressure shocks arising during the operation of the apparatus.
A further aspect of this purpose is to provide a design, which gives a uniform pressure distribution over the delimiting surfaces of the gas chamber.
Another aspect of this purpose is to provide a design that is adapted to protect a sealing, arranged between a dielectric and an opposite delimiting surface, from wear as a consequence of the reactive action of the ozone.
According to a first aspect of the present invention an ozone generator B referred to, for these purposes comprising a unit, in which unit a high voltage electrode and an electrically isolating element, preferably a dielectric element, are joined, and a chamber which is delimited by said dielectric element and by an earth electrode. The invention is, according to the first aspect, characterized by the ozone generator being arranged to operate with pressure equilibrium, whereby a pressure change in said chamber is arranged to act with equal force on opposite sides of said unit.
According to a second aspect of the invention an ozone generator is referred to, comprising a high voltage electrode, and also a first and a second dielectric element, arranged on opposite sides of said high voltage electrode. These dielectric elements are on opposite sides of said high voltage electrode arranged in sealed connection with a first and a second earth electrode, respectively, whereby the respective earth electrodes are arranged to delimit a first and a second sealed chamber, respectively, towards said first and second dielectric element, respectively. More specifically according to a third aspect of the invention, an ozone generator is thus referred to, wherein a high voltage electrode is located centrally between two uniform sealed chambers, and wherein each one of the chambers on one side is delimited from said high voltage electrode by a dielectric, and on another side by an earth electrode. With this arrangement the ozone generators sensitive dielectric element is exposed to equal gas pressure and gas pressure variations from opposite sides, whereby the pressure is equalized.
According to a fourth aspect an ozone generator is referred to, comprising a high voltage electrode and a dielectric, which dielectric delimits a sealed chamber to an opposite wall with an intermediate endless sealing. According to the fourth aspect, the invention is characterized by a recess being formed in an outer part of the chamber, endlessly extending adjacent said sealing, in which recess an inlet to said chamber emerges, whereby the chamber presents a larger depth in said recess than in its central part. Preferably an outlet from said chamber, intended for output of ozone, is arranged with an orifice at the central part of the chamber. With this arrangement the supplied oxygen gas or gas rich in oxygen is made to first fill said recess, in which the smallest resistance for the gas to diffuse is provided, and thereafter to diffuse towards the central parts of the chamber. With a uniform gas flow, which flow due to the locations of the inlet and outlet is directed from the periphery of the chamber to its center, oxygen which first fills the chamber close to the sealing will protect the same from the ozone generated in the chamber.
According to a preferred embodiment of the present invention the ozone generator comprises a pressure compensation admitting unit, which has been joined together with at least two plates of a dielectric material and an electrode present between said plates, on which electrode a high frequency alternating current with high voltage is applicable, and two sealed spaces for ozone generation on opposite sides of said unit, whereby the respective sealed space, on the side opposite the plate of dielectric material, is delimited by an earthed and cooled electrode, via which oxygen gas or gas rich in oxygen is supplied to the space and ozone is conducted away from the same.
By this arrangement a compact design with minor space requirements is obtained, still having high efficiency without damage or sealing problems at e.g. the unit comprising the plates of dielectric material and the electrode on which a high frequency alternating current with high voltage is applicable, since this unit at the same time is influenced by an overpressure and pressure shocks from two opposite sides, respectively, and by its form moreover forces these overpressures and pressure shocks, respectively, to compensate, i.e. equalize, each other. The compensation of said overpressure and pressure shocks, respectively, which may originate during operation of the apparatus gives stability to the apparatus and thereby an increased conversion efficiency for the same.
The present invention also refers, according to a fifth aspect, to a method for ozone generation comprising the steps of supplying oxygen or gas rich in oxygen to a first chamber, and applying a high frequency alternating current with high voltage to a high voltage electrode for the purpose of causing a discharge in the first chamber over a dielectric to an earth electrode. The method is characterized by pressure changes in the supplied gas being compensated by the gas pressure being forced to operate to the same extent on opposite sides of a compact unit comprising said dielectric. By compact is here meant that the included components in the unit between themselves are in mechanical connection without any intermediate spaces, whereby the unit substantially constitutes a non-compressible body.
More exactly, according to a sixth aspect of the present invention, a method for ozone generation is referred to comprising the steps of oxygen gas or gas rich in oxygen under pressure being conducted from a common source into two uniform sealed chambers, which chambers are delimited from each other by a unit, which unit comprises two dielectric elements and between them a high voltage electrode, a high frequency alternating current with high voltage being applied on said high voltage electrode, existing oxygen in the chambers thereby being converted to ozone by electric discharges between said high voltage electrode and separate earth electrodes, where each earth electrode respectively delimits one chamber, respectively, on opposite side of the respective dielectric element.